1. Technical Field of the Invention
The present invention relates to a cable-type steering device in which a steering wheel and a gear box are connected to each other by flexible cables such as Bowden wires.
2. Description of Related Art
In a conventional steering device for a vehicle, a steering shaft having a steering wheel at an upper end thereof is connected at its lower end to a gear box, so that the steering torque inputted to the steering wheel is transmitted through the steering shaft to a rack and pinion mechanism which is mounted within the gear box.
However, if the steering wheel and the gear box are connected to each other using the steering shaft, the position of the steering wheel relative to the position of the gear box is relatively fixed and there is little freedom in selecting a preferred position for each element. For this reason, there is encountered a problem in that the degree of freedom of design is substantially limited, and further, the gear box cannot be commonly used in a right-hand steered vehicle and a left-hand steered vehicle. Moreover, another problem is that vibrations inputted to a tire from a road surface and the vibration of an engine are inputted to the steering wheel through the steering shaft and hence, the level of audible sound or silence within a vehicle compartment and the riding comfort are impeded by such vibrations.
Therefore, there is a proposed cable-type steering device which employs a flexible transmitting means such as Bowden wire and the like in place of the conventional steering shaft (see Japanese Patent Application Laid-open No.8-2431).
If the construction of the proposed cable-type steering device is used, the position of the steering wheel relative to the position of the gear box can be freely selected and moreover, the vibration of the gear box is difficult to be transmitted to the steering wheel and hence, the above-described problems can be solved.
In such cable-type steering device, the steering torque inputted from the steering wheel is relatively small with an upper limit value restricted by a driver's physical strength. However, a road surface reaction torque produced when wheels are brought into contact with a curb may reach a magnitude of 10 times as large as the steering torque in some cases. Therefore, if the cable-type steering device is designed to be able to withstand such road surface reaction torque, there is encountered a problem that it is necessary to increase the strength of the cable-type steering device, resulting in increased weight and size and an increased cost of manufacture. Another problem is that if a large road surface reaction torque is transmitted to the steering wheel without being buffered, the feeling of a driver grasping the steering wheel is degraded.